Authors: L. Busoni, S. Esposito
Adaptive Optics is one of the most important techniques today for ground-based telescopes. All the next generation telescopes, the extremely large telescopes with diameters ranging from 25 to 40m, have been designed to have AO systems in place and working for most of the observations if not all. The largest of these telescopes the 40m European Extremely Large Telescope is considered an adaptive telescope and features a deformable mirror of 2.5m diameter with about 6000 actuators. The most ambitious and challenging AO systems are those aiming to provide a wide field correction of the atmospheric perturbation. To do that a tomographic approach is required. Multiple reference sources, multiple deformable mirrors and multiple wavefront sensors with different type of reference sources are the key elements of such systems. They are all operated together to provide a 3D measurement and correction of the atmospheric phase perturbation. The challenges in design and built a similar tomographic system for the ELT are briefly described in the talk from assessing tomographic fundamental limitations to engineering of an optomechanical system spanning a volume of 6x6x3 m and 30 tons of weight. Future directions of general developments for Astronomical MCAO systems as identified during the MAORY design are briefly introduced at the end of the talk.